This invention relates to an absorption refrigerator of double effect type and particularly to an arrangement of such an absorption refrigerator provided with a flash type heat exchanger.
Well-known absorption refrigerators are mainly of a single effect type comprising a generator for heating a weak solution to generate vapor of refrigerant, a condenser for condensing and liquidizing the vapor of refrigerant, an evaporator for evaporating the liquidized refrigerant to provide cooling, and an absorber for absorbing the vapor of refrigerant of the evaporator into a strong solution.
However, the thermal efficiency (refrigeration ability/amount of heat) of such a single effect type absorption refrigerator is relatively low and ordinarily about 0.6 in practice and it is, therefore, very important to increase its thermal efficiency under such a circumstance that the cost of fuel is becoming high in the recent time.
With a view to increasing the thermal efficiency, there has recently been put into practice a so-called double effect type absorption refrigerator in which a further generator is additionally provided in the single effect type absorption refrigerator such that the high temperature vapor of refrigerant generated in the first-mentioned generator is utilized to heat the further generator.
In general, the double effect type absorption refrigerator comprises a high temperature generator, a low temperature generator, a condenser, an evaporator, an absorber, a high temperature heat exchanger and a low temperature heat exchanger. In the high temperature generator, a refrigerant dissolved solution, such as an aqueous solution of lithium bromide (hereinunder referred to as solution) is heated by heating means to discharge the dissolved refrigerant as vapor. The discharged refrigerant vapor is fed through a pipe to the low temperature generator to heat the weak solution supplied from the absorber to be described below in more detail, and while the refrigerant in the weak solution is discharged therefrom the vapor of the solution is cooled by the latent heat due to the evaporation and condensed and liquidized to be fed to the condenser. The refrigerant vapor produced in the low temperature generator is supplied through a pipe to the condenser and cooled by cooling means thereof and then condensed and liquidized. This liquidized refrigerant is fed through a pipe to the evaporator to be sprayed therein, thereby cooling its cooling means to exert a cooling function and thus converted to the refrigerant vapor and then fed through a pipe to the absorber which is cooled by the cooling means. On the other hand, the solution concentrated by discharging the refrigerant vapor in the high temperature generator is fed through a pipe to the high temperature heat exchanger to make heat exchange with the low temperature weak solution supplied from the absorber, thereby suitably lowering its temperature, and then fed to the low temperature heat exchanger together with the strong solution derived from the absorber by way of the low temperature generator in which refrigerant is discharged from the solution. In the low temperature heat exchanger, the solution makes heat exchange with the low temperature weak solution derived from the absorber through a pipe, thereby lowering its temperature, and then flows through a pipe to the absorber which is cooled by cooling means. In such a manner, solution sprayed in the absorber absorbs the refrigerant vapor supplied from the above-mentioned evaporator through the pipe, and provides a low temperature weak solution. This solution is further directed through a pipe to the low temperature heat exchanger in which it in turn makes heat exchange with the strong solution derived from the above-mentiond high and low temperature generators, thereby appropriately rising in its temperature, and then is branchedly transported through pipes to the low temperature generator and the high temperature heat exchanger. The solution transported to the high temperature heat exchanger makes heat exchange therein with the high temperature strong solution derived from the high temperature generator through the pipe, thereby rising in its temperature, and then flows back to the high temperature generator through a pipe.
In this manner, the double effect type absorption refrigerator is arranged such that the heat supplied from the exterior is twice utilized in the high and low temperature generators and so the thermal efficiency increases up to 50 - 60% in comparison with the single effect type refrigerator. Furthermore, the double effect type refrigerator is arranged such that the high and low heat exchangers provided in the solution circulation system between the high and low temperature generators and the absorber make heat exchange between the solutions flowing through the system to increase the thermal efficiency and are indispensable to the double effect type absorption refrigerator from the point of reduction of energy. The high and low temperature heat exchangers have ordinarily been formed by multi-tubular type heat exchangers in which heat exchange is made by thermal contact of two fluids through other heat transmitting means.
As described above, the double effect type absorption refrigerator is very useful from the point of thermal efficiency, but it is necessary to increase the generating temperature of the high temperature generator to some extent in order that the refrigerant vapor generated in the high temperature generator is used as a heating source of the low temperature generator. Therefore, there are the following problems;
(1) As is well known, the high temperature and high concentrated aqueous solution of lithium bromide has high corrosiveness. Therefore, the parts of the high temperature generator can not be prevented from corrosion and it is difficult to maintain their long durability.
(2) The pressure of the high temperature generator rises due to increase in the generating temperature. More specifically, the difference in pressure throughout the entire refrigerator is larger than that in the single effect type refrigerator. Therefore, the transportation of fluids within the absorption refrigerator, such as circulation of solutions, greatly increases the economic load.
(3) In view of the necessity of high generating temperature, the temperature level of the heat source to be used in the refrigerator is limited to its high region. In order to effectively use the waste heat from various plants from the point of recent reduction of energy, low temperature operation of the absorption refrigerators is strongly desired in this technical field. In this respect, it is desired that the working temperature of the generator is lowered without reducing the refrigerating capacity of the refrigerator, but conventional double effect type refrigerators can not satisfy such requirements.
In order to solve the above-mentioned problems of the conventional double effect type absorption refrigerators, it is necessary to reduce the concentration of solution in the high temperature generator to lower the working temperature thereof. In conventional absorption refrigerators, however, mere reduction in the concentration of solution can lower the working temperature of the high temperature generator, but increases the pressure of the absorber, thereby not enabling to prevent great reduction in the cooling ability. To prevent this, there are proposed such methods that the heat transmitting surfaces of elements constructing the absorption refrigerator are formed by high performance heat transmitting surfaces, such as gilled tubes, or that the heat transmitting surface is increased. However, the former method not only increases the manufacturing cost of refrigerators, but also makes a change with the lapse of time of the heat transmitting performance, and the latter method must make apparatus large in size and make its capacity small for its size. Therefore, these methods are not always desirable from the industrial point of view.
To solve those problems, means for adjusting the concentration of solution are provided in the solution circulation system between the generators and the absorber to adjust the concentration of solutions relative to each other such that the concentration of solution supplied from the absorber to the high temperature generator is lowered without varying the concentration of solution in the absorber. With this, it is possible to lower the working temperature of the high temperature generator without reducing the cooling ability.
With conventional solution heat exchangers provided in the solution circulation system, however, it is impossible to adjust the above-mentioned relative concentration of solutions, but the above-mentioned requirements can be satisfied by the application of the flash type heat exchange system used in the chemical industry. More specifically, the adjustment of the solution concentration can be made by the provision of means having a function for flashing the strong solution fed from the generator to the absorber as well as a function for absorbing the vaporized refrigerant produced in the above-mentioned step into the weak solution fed from the absorber to the generator. Accordingly, by the provision of such concentration adjusting means in the solution circulation system the concentration of solution in the high temperature generator can be lowered without varying the concentration of solution in the absorber, thereby attaining low temperature operation of the high temperature generator. Moreover, in such concentration adjusting means the heat flow is caused simultaneously with the movement of the vaporized refrigerant and thus heat recovery can be made from the high temperature strong solution to the low temperature weak solution and this is effective from the point of increasing the thermal efficiency of the refrigerator.